The polybutylene terephthalate resin (PBT) is utilized in a wide variety of fields, such as machine mechanism component parts, electrical/electronic component parts, automotive component parts, etc., making most of its excellence in characteristics, such as injection moldability, mechanical properties, etc.
As PBT is essentially combustible, PBTs are required to have safety against flames, that is, flame retardancy, and in many cases need to have such high degrees of flame retardancy as to indicate V-0 in the UL 94 standard, as well as balance of general chemical and physical properties, in order to use the PBTs as industrial materials such as machine mechanism component parts, electrical/electronic component parts, automotive component parts, etc.
The method for imparting flame retardancy to the PBT is generally a method in which a halogenated organic compound as a flame retardant and an antimony compound as a flame retarding assistant are compounded into a resin. However, this method has a tendency toward large amounts of smoke produced during combustion.
Furthermore, with a rise of environment consciousness, there are movements having concerns about the influences of halogenated flame-retardant materials on the environments.
Therefore, recently, use of a flame retardant that contains none of such halogens has become desired.
As a method for flame-retarding a thermoplastic resin without using a halogenated flame retardant, addition of a hydrated metallic compound, such as aluminum hydroxide, magnesium hydroxide, etc., has been widely known. However, the aforementioned hydrated metallic compound needs to be added in a large amount in order to attain sufficient flame retardancy, and this method has a drawback of losing an essential property of resin.
As a method for flame-retarding a thermoplastic resin without using such a hydrated metallic compound, addition of red phosphorus is disclosed in Japanese Patent Application Laid-Open Publication No. SHO 51-150553, Japanese Patent Application Laid-Open Publication No. SHO 58-108248, Japanese Patent Application Laid-Open Publication No. SHO 59-81351, Japanese Patent Application Laid-Open Publication No. HEI 5-78560, Japanese Patent Application Laid-Open Publication No. HEI 5-287119, Japanese Patent Application Laid-Open Publication No. HEI 5-295164, Japanese Patent Application Laid-Open Publication No. HEI 5-320486, Japanese Patent Application Laid-Open Publication No. HEI 5-339417, etc.
These are useful flame-retardant resin materials not employing a halogenated flame retardant, but have peculiar coloration so that the color tone of the products is limited, and therefore has the challenge of limited uses.
Furthermore, in Japanese Patent Application Laid-Open Publication No. HEI 3-281652, Japanese Patent Application Laid-Open Publication No. HEI 5-70671, Japanese Patent Application Laid-Open Publication No. HEI 7-233311, Japanese Patent Application Laid-Open Publication No. HEI 8-73713 and Japanese Patent Application Laid-Open Publication No. HEI 10-120881, compounding an aromatic phosphoric acid ester and melamine cyanurate is disclosed.
Theses are useful flame-retardant resin materials not employing a halogenated flame retardant, but have a problem of occurrence of a bleedout in which an aromatic phosphoric acid ester seeps out to a formed article surface or of bringing about metal pollution.
Furthermore, in Japanese Patent Application Laid-Open Publication No. HEI 10-77396, Japanese Patent Application Laid-Open Publication No. HEI 10-147699, Japanese Patent Application Laid-Open Publication No. HEI 10-182955, Japanese Patent Application Laid-Open Publication No. HEI 10-182956, and Japanese Patent Application Laid-Open Publication No. 2000-26710, compounding a styrene based resin into a composition in which a resin, such as a PBT, a polyphenylene ether, etc., and a phosphoric acid ester are compounded is disclosed.
These are useful flame-retardant resin materials not employing a halogenated flame retardant, but have problems; for example, due to the compounding of such a resin as a polyphenylene ether, etc., the mechanical strength deteriorates, the fluidity at the time of injection molding deteriorates, the formed article colors yellow, and the hydrolysis resistance and the metal pollution characteristic are poor, and the uses are limited.
Furthermore, in Japanese Patent Application Laid-Open Publication No. HEI 2000-212412, compounding a polyester, and an organic phosphorus based flame retardant including a phosphoric acid ester, as well as a glass fiber, and a vinyl based resin is disclosed.
These are useful flame-retardant resin materials not employing a halogenated flame retardant, but have the challenge of metal pollution characteristic and deterioration in hydrolysis resistance due to the organic phosphorus based flame retardant.
Furthermore, in Japanese Patent Application Laid-Open Publication No. HEI 2001-49096, compounding a flame retardant composed of a phosphorus-containing compound including a phosphoric acid ester, and specific aromatic resin, aromatic nylon, polycarbonate resin, polyalylate resin, polyepoxy resin and polyphenylene ether resin into a resin component including a polyester based resin and a styrene based resin.
The aforementioned resin component including a polyester based resin and a styrene based resin is a resin component useful for improvement in moldability related to warpage, etc., and the aforementioned flame retardant is a useful flame retardant not employing a halogenated flame retardant, but does not have effect on the challenge of the metal pollution characteristic and deterioration in hydrolyzability due to the phosphorus-containing compound.
From what is described above, although the organic phosphorus based flame retardant, such as a phosphoric acid ester, etc., is a useful flame retardant as a method for flame-retarding the PBT by a non-halogenated flame retardant, a flame-retardant PBT resin composition that does not cause the metal pollution and the deterioration in hydrolysis resistance due to a phosphoric acid ester has been desired.
Particularly, formed articles for fusers of printers and copiers, flyback transformers, focus cases, electromagnetic switches, and breakers are often required to have excellent performance in relation to metal pollution, hydrolysis resistance and flame retardancy.
Furthermore, a phenomenon in which if voltage is applied to a formed article, etc., carbonization of the formed article progresses and results in ignition is termed tracking. Many formed articles of the PBT are used under high voltage modification. For example, as for the aforementioned formed articles for fusers of printers and copiers, electromagnetic switches, and breakers, etc., formed articles having excellent flame retardancy and a relative tracking index of 400V or higher, and preferably 600V or higher, are desired.
It would therefore be advantageous to attain highly reliable flame-retardant polybutylene terephthalate resin composition and formed article in which a non-halogenated flame retardant is compounded with a polybutylene terephthalate resin, and which have high degrees of flame retardancy and tracking resistance, and which are unlikely to allow occurrence of metal pollution or deterioration in hydrolysis due to a phosphoric acid ester.